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Heathkit SB-102 Information, troubleshooting, etc.

So I have my first HF rig, itself a gift from XYL's father. The rig is a Heathkit SB-102, which he insists is a 'piece of crap,' 'junker rig' and other such similar remarks. Considering it's the only HF radio I have ever owned, I'm not in any position to respond, but I am going to attempt to bring it back to full operating condition.

This is what I know about the rig:

The bad:
1. It has no audio on the LSB setting at all.
2. I don't have a key, but when testing it, no relay would close on CW mode and there is no output on CW mode.
3. The original speaker is gone.

The good:

1. It will both TX and RX on 20m USB. XYL's father made contact with someone in Canada with it about 2 weeks ago.
2. The original mic and power supply were both included and work.
3. It was free.
4. It worked at one time and nobody's been inside it since then, so presumably, it was built correctly.

I have already PMed a few of you but I'd like to post this in the open forum for any insight. For the time being, I am mostly interested in information that can get me started with troubleshooting this thing. I don't know very much about troubleshooting a radio, although I did spend 4 years in maintenance and am confident in my electrical troubleshooting skills. That said, vacuum tubes are something I'd previously only seen in pictures in a textbook and old films, so I am in uncharted territory. A manual that explained the theory of operation of the various circuits would be a good start.

Advice on where to begin and what I'll need besides a basic multimeter would be a good start. I am not in a hurry and would like to take my time and get this thing back working properly, and then I'll try to get on the air with it.

Do you have the manual for the rig? If not get a hold of one. For the most part Heathkit has very good instructions for preliminary checks, alignment, and troubleshooting. A good place to start. However, you'll always find those weird problems that defy explanation! See my post on meter not zeroing problems!!!

I'm going to print it and read it from cover to cover soon. I bet that'll be a good start.

It's an excellent start especially if you have the complete assembly and operations manual. The theory of operations is well explained and there are measurement points both voltage and resistive that will be very helpful.
Having more test equipment would help. An oscilloscope helps with transmit problems and some reception problems as well. A small signal generator would be good and an old VTVM would be more responsive to the quick tuning peaks and dips then a DMM. You can still use a DMM with success but it takes a bit more skill to do that. The DMM will have just about the same loading on a circuit then a VTVM and the DMM will give you some very good accurate readings as well.
Now the LSB isn't working. That usually indicates a problem with the LSB carrier generator oscillator but it could just as easily be a connection problem or a bad switch. Usually the rigs in the era of the SB-102 need to be cleaned up on the relay contacts and the switches, potentiometers and other connective surfaces including the grounding points for the circuits.
One thing to do is to follow the assembly portion of the manual. Perform each step as though you were constructing it for the first time. Check the resistors for proper value when you can and use the resistance chart provided. The reason to do that is because there are usually other resistive devices that will change the reading you would get from just a free component that is not installed in the circuit. In every case the resistance will read at or lower then the value of the component. If it reads higher something is wrong.
Okay, enough of this. As you can tell from your list of Good you'll find #3 really isn't true in the long run. The SB-102 is an okay rig and you'll have loads of fun with it.
Any speaker of 8 ohms or so will work fine on the SB-102 or you could use headphones. Lots of in and out phono plugs on the back of the rig to do things with.
One last thing. Be careful when working inside the SB-102. There are voltages that will raise your hair, knock you flat, injure you or even cause death. Use the utmost caution. Read the safety tips in older ARRL Handbooks on how to work on tube circuits and higher voltage. If you have no clue then get an asistant that knows what to do and can direct you. Make sure whoever you have around you when you are working on the unit they are aware of what to do in case of a problem and know the proper first aid skills. Try as much as you can to never work alone or when you're tired. Follow these steps and you'll make it just fine.
Have fun
73
Gary

So I have my first HF rig, itself a gift from XYL's father. The rig is a Heathkit SB-102, which he insists is a 'piece of crap,' 'junker rig' and other such similar remarks. Considering it's the only HF radio I have ever owned, I'm not in any position to respond, but I am going to attempt to bring it back to full operating condition.

This is what I know about the rig:

The bad:
1. It has no audio on the LSB setting at all.
2. I don't have a key, but when testing it, no relay would close on CW mode and there is no output on CW mode.
3. The original speaker is gone.

The good:

1. It will both TX and RX on 20m USB. XYL's father made contact with someone in Canada with it about 2 weeks ago.
2. The original mic and power supply were both included and work.
3. It was free.
4. It worked at one time and nobody's been inside it since then, so presumably, it was built correctly.

I have already PMed a few of you but I'd like to post this in the open forum for any insight. For the time being, I am mostly interested in information that can get me started with troubleshooting this thing. I don't know very much about troubleshooting a radio, although I did spend 4 years in maintenance and am confident in my electrical troubleshooting skills. That said, vacuum tubes are something I'd previously only seen in pictures in a textbook and old films, so I am in uncharted territory. A manual that explained the theory of operation of the various circuits would be a good start.

Advice on where to begin and what I'll need besides a basic multimeter would be a good start. I am not in a hurry and would like to take my time and get this thing back working properly, and then I'll try to get on the air with it.

How did you test CW mode if you didn't have a CW key? I'll assume you used a 1/4" mono plug and shorted the plug's terminals. If that's true, did you hear the CW side tone in the speaker? If not, even by adjusting the side tone level control inside the transceiver, then the side tone oscillator and/or side tone amp circuits are NOT working. If TUNE mode position keys the transmitter (relays energize) then the VOX Relay Amp circuit is working.

Connect a scope to pin 9 of V15B (CW side tone amp). Set the Mode switch to CW, short the CW key socket terminals, you should see the side tone sine wave on the scope. If you don't see the sine wave then suspect V15 (6EA8) as being bad. If you see the sine wave, connect the scope to pin 7 of V17A (VOX AMP). You should see the same side tone sine wave as you did at pin 9 of V15B. If you don't then suspect V15 as being bad. V15 contains a pentode and triode section. The pentode section is the CW oscillator and the triode section is the side tone amp and is turned ON by placing the Mode switch in CW (grounds the cathode of V15A turning the CW side tone oscillator ON). With a key inserted into the CW socket and pressed (shorts the CW socket to ground), the "grid block" keying voltage at pin 9 of V15B is reduced to a point where V15B is turned ON, allowing the CW side tone signal to be amplified by V15B and fed to the VOX AMP and the receive audio amp. This is explained in the SB-102's manual's Circuit Description section.

Loss of audio in LSB can be caused by a failure in the LSB carrier generator crystal. If you have a frequency counter or can borrow one, connect the counter to the center pin on the CAR NULL pot. The frequency should be 3393.6Khz. You should also see the same signal a V13C's pin 9 (Product Detector). The Carrier Generator V16A/B provide the receive "BFO" signal to V13C Product Detector. The receiver uses the "USB" Carrier Generator crystal as the source fo the BFO in CW receive but switches to the CW crystal in CW transmit (see the schematic) so don't be confused if you don't see 3395.4Khz on a frequency counter with the Mode switch set to CW in receive. The SB-102's "Circuit Description" section will show you how this works.

The SB-102 is a great old radio. There is very little that can't be repaired with patience and persistence and the full manual. The manual lists every tool and instrument needed to build and test the radio, with a couple exceptions.

The key to success is working in a methodical manner. Use a note book to record your daily work, findings, parts needed, etc. It will be helpful as a memory aid days or weeks later. A digital camera is now a wonderful aid as well before disassembly.

The one 'new' instrument that will be invaluable is an LCR tester. This is used to test caps, inductors and resistor values for out of tolerance. Takes the guesswork out of things, especially for caps. Buy few rolls of solder wick, and some sort of vacuum de-soldering device, bulb or spring, or the deluxe Hako gun. Get a roll of genuine Kester 44 solder. The quality stuff is definitely better and doesn't cost much more. A small bottle of liquid flux will help make reliable connections on oxidized parts.

I advise against trying for a 'Hail Mary" play in trying to fix the radio in one shot. Work thru the manual board by board and you will end up with a reliable radio that works right. The main problems you will face are: bad solder joints, bad solder joints, out of tolerance parts, board grounding. Oh, and solder joints.

Most things can be cleaned at the sink with warm water, soft brush and dilute soap or dilute Krud Kutter. Mask off coils, or obvious water sensitive parts with tape, dry in a warm place overnight.

Take your time and you will get to enjoy the journey of (re)building a Heathkit like thousands of hams over the previous 65 years and you will end up with a radio ready to run for another twenty years. 73, bill

How did you test CW mode if you didn't have a CW key? I'll assume you used a 1/4" mono plug and shorted the plug's terminals. If that's true, did you hear the CW side tone in the speaker? If not, even by adjusting the side tone level control inside the transceiver, then the side tone oscillator and/or side tone amp circuits are NOT working. If TUNE mode position keys the transmitter (relays energize) then the VOX Relay Amp circuit is working.

I tested it with XYL's father's CW key.

Relays do not energize in tune mode or CW mode.

Although the CW mode isn't at the top of my list for things to repair, it doesn't work, at all.

Short pin 8 of V12 to ground, the relays should energize. If they do then measure the PTT voltage, it should be 14VDC. A loss of PTT voltage can be caused by a break in the wiring between pin 8 on V12 and the microphone PTT terminal. A break in the DC path between pin 8 of V12 and the PTT terminal and Mode switch wafer 2F terminal 20 (both are in parallel) can cause loss of "TUNE" mode and PTT.

The PTT voltage is 14VDC, measured at the microphone's PTT terminal, and the voltage should drop to zero when the Mode switch is set to TUNE.